Voltage and displacement measuring apparatus and probe

ABSTRACT

A voltage and displacement sensitive probe with an electro-optic crystal, electrically conductive transparent films and adhered to a pair of parallel surfaces on the electro-optic crystal, a transparent elastic film which circumferential portion is bonded to the frame and which is symmetric with respect to any plane through the axis thereof, a probing needle bonded at its reflective bottom surface to the central portion on the film, a holder for holding the electro-optic crystal and the transparent elastic film via frame concentrically, a lead for grounding, and electrically conductive films for connecting between the films. Displacement detection of the probing needle is based upon the change in the length of the path of the light travelling through the electro-optic crystal being reflected by the surface and travelling in reverse direction. Voltage detection of the probing needle is based upon the phase difference between the two linearly-polarized light components.

This is a divisional of application Ser. No. 08/282,265 filed Jul. 29,1994, now U.S. Pat. No. 5,677,635.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a voltage & displacement measuringapparatus and its probe for measuring the position and voltage of amicro structure such as a wiring on a semiconductor chip.

2. Description of the Related Art

In order to measure voltages in the fine wiring on semiconductorintegrated circuits, there are some measuring instruments using anelectron beam, namely, an electron beam tester, and using a light beam,namely, a light beam tester.

An electron beam tester emits an electron beam on to a fine wire to bemeasured (measuring point) and detects the quantity and energy ofsecondary electrons emitted from this measuring point. The voltage ismeasured based upon this detection.

A light beam tester uses the electro-optic effect of crystals; byradiating a light beam into an electro-optic crystal which is positionednear the measuring point and detects the change of the polarizationstatus of the light passed through the crystal, and the voltage ismeasured based upon this detection.

For measuring the waveform of a voltage pulse with a short leading edgeor trailing edge time such as 1 nano-second or less, with an electronicor light beam tester, a pulsed beam is used to sample the voltage at thetime when the beam is irradiated.

With an electron beam tester, on the one hand, it is necessary to raisethe spatial resolution by narrowly constricting the electron beam incomparison with the width of the wire at the measuring point while, onthe other hand, it is also necessary to raise the time resolution bysetting a short pulse width for the electron beam, in order to respondto rapid changes in the waveform being measured. Because of this, thenumber of electrons in the pulse beam is reduced and this, in turn,reduces the number of secondary electrons generated at the beamirradiation points, resulting in a deterioration of the S/N ratio (thevoltage resolution is reduced). To deal with this, a cyclical testsignal may be supplied to the semiconductor integrated circuit which isbeing measured, and a pulse beam is then radiated in the same phase forseveral cycles, and the average value of the detection signal can beused to improve the S/N ratio. However, this measuring procedurerequires a long time.

Since the S/N ratio is reduced when the pulse width of an electron beamis narrower, and since the secondary electron detection signal spreadsin the direction of time because there are differences in running timeamong secondary electrons, the upper limit of time resolution at presentis approximately 5 pico-seconds and the realization of higher timeresolution is difficult to achieve.

The light beam tester provides a higher time resolution, such as 0.5pico-seconds, and a higher voltage resolution, namely higher S/N ratio,over the same values obtained for electron beam tester. However, sincethe spatial resolution is limited by the wavelength of the light, it isdifficult to measure the voltage in a fine wire. Actually, it ispossible to measure the voltage in wire having a diameter of 1 μm ormore, at present, but it is difficult to measure voltage in any wirehaving a diameter less than that.

As has been explained, the electron beam tester provides good spatialresolution but is unsatisfactory in time while, in contrast, resolutionand measuring time, the light beam tester excels in time resolution andmeasuring time, but is unsatisfactory in spatial resolution. Namely,these two types of testers have opposite and complementary advantagesand shortcomings.

Furthermore, when probing a narrow wire on the order of sub-microndimensions, with a light beam tester, the electrical contact with thewire is insufficient.

A probe for a voltage and displacement measuring apparatus which canimprove the space and time resolution, would be conceived, the schematicstructure of which is shown in FIG. 19.

The semiconductor chip 10 has the bonding wires 11, 12 connecting thepad on its surface and the inner lead (not shown).

The upper end of the cantilever 22 of the probe 20, is bonded to thelower end of the substrate 21 and the electrically conductive probingneedle 23 is bonded to the lower end of the cantilever 22. Thecantilever 22 and the probing needle 23 are of the type that are used inAFM (Atomic Force Microscope) and the cantilever 22 has the springconstant of 1 to 100 N/m and is, therefore, soft enough to measure. Thediameter of the probing needle 23 at the top is very small (e.g., 50nanometers or less). When the probing needle 23 is placed close to thesemiconductor chip 10, a distance in the order of nanometers, or whenthe probing needle 23 contacts the semiconductor chip 10, displacementoccurs in the cantilever 22. Displacement in the direction of the heightof the probing needle 23 is measured by irradiating a laser beam fromthe laser 24 on to the upper surface of the lower end of the cantilever22 and by detecting its reflected light with the PSD (Position SensitiveDetector) 25. While measuring this displacement, an X-Y scanning of theprobe 20 relative to the semiconductor chip 10 is performed by applyinga piezoelectric actuator. During the X-Y scan, the displacement of theprobing needle 23 can be constant by controlling the Z-directionpiezoelectric actuator, and an image of the concave-convex surface ofthe chip 10 can be obtained based upon the driving signal for theZ-direction piezoelectric actuator. This image will have a spatialresolution in the order of nanometers and the position of the probingneedle 23 on the wire to be measured can be determined with an accuracyin the order of nanometers based upon this image.

In order to detect the potential at the measuring point, theelectro-optic crystal 26 is bonded onto the substrate 21. The lowersurface of the electro-optic crystal 26 is electrically connected withthe probing needle 23 by an electrically conductive film and theelectrically conductive transparent film which is adhered to the uppersurface of the electro-optic crystal 26 is grounded. When the probingneedle 23 contacts the measuring point on the wire or approaches themeasuring point to within a distance on the order of nanometers, anelectric field, due to the potential of the wire, is applied to theelectro-optic crystal 26. The laser beam from the laser 28, which hasbeen reflected by the mirror 27, enters the electro-optic crystal 26 andthen the light reflected from the bottom of the electro-optic crystal 26via a polarization beam splitter (not shown) is detected by thephotodetector (not shown). The potential at the measuring point ismeasured based upon this detection.

However, since the tip of the probing needle 23 must either contact thesemiconductor chip 10 or be in and after close proximity to it, there isa limit to the angle of inclination of the substrate 21 relative to thesemiconductor chip 10. In addition, the probing needle 23 must scan thesemiconductor chip 10 in such a manner that the substrate 21 does notinterfere with the bonding wires 11 and 12. Accordingly, the probingneedle 23 cannot scan in the range R shown in FIG. 19, resulting in anarea that cannot be measured.

Also, since a mechanism is required that rotates the probe 20 or thechip 10 in correspondence with the position of the probe 20 on the chip10 so that the probe does not interfere with the bonding wires, thestructure and operation of the apparatus become complicated.

Furthermore, since an optical system for displacement measurement and aseparate optical system for voltage measurement are required, thestructure and the adjustment thereof become complicated.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a voltageand displacement measuring apparatus and a probe which can performmeasurement without interfering with bonding wires on the sample.

Another object of the present invention is to provide a voltage anddisplacement measuring apparatus and a probe which can achievesimplification of the structure and operation of the apparatus.

According to the first aspect of the present invention, there isprovided a voltage and displacement sensitive probe comprising: a holderhaving a hole being approximately symmetrical with respect to aplurality of planes through the axis thereof; an electrically conductiveelastic film located inside the hole, the outer end of the elastic filmbeing bonded to the holder, the elastic film being approximatelysymmetrical with respect to a plurality of planes through the axis ofthe hole; an electrically conductive probing needle located under theelastic film with the tip of the probing needle downward and beingcoupled to the central portion of the elastic film; voltage informationgenerating means, coupled to the holder at a position over the probingneedle and connected electrically with the probing needle, forgenerating a voltage information of the probing needle against areference potential in response to light beam entered therein, thevoltage information being a form of either a photo-signal or anelectrical-signal; and displacement information generating means,coupled to the holder at a position over the probing needle, fordetecting an axial displacement information of the probing needle, theaxial displacement information having a form of either a photo-signal oran electrical-signal.

With this arrangement, since each of the hole of the holder and theelectrically conductive elastic film is approximately symmetrical withrespect to a plurality of planes through the axis thereof, theelectrically conductive elastic film is inside the hole, the outer endof the elastic film is bonded to the holder and the probing needle ispositioned on the axis of the probe, the axis of the probe can be setvertical to the surface of the sample and measurement can be performedwithout the probe interfering with the bonding wires on the sample.

Furthermore, although in the case of the cantilever type probe shown inFIG. 19, a mechanism that rotates the probe or the sample is required toprevent the probe from interfering with the bonding wires and the likeon the sample, the first aspect of the present invention eliminates thenecessary for such a mechanism. As a result, the structure and operationof the voltage & displacement measuring apparatus that apples this probecan be simplified.

In the first mode of the first aspect of the present invention, thevoltage information generating means is a voltage/phase-differenceconversion means including: an electro-optic crystal having first andsecond surfaces which are parallel to one another and arrangedvertically to the axis of the hole; a first electrode being atransparent film adhered to the first surface; a second electrodeadhered to the second surface and connected electrically with theprobing needle; a lead for supplying the reference potential to thefirst electrode; and reflective means for reflecting a light beamtraveling from the first electrode through the electro-optic crystal andback.

With this arrangement, the voltage between the first electrode and thesecond electrode can be detected based on the phase-difference betweentwo vertical components of linearly polarized light, thephase-difference created by the light beam traveling through theelectro-optic crystal, being reflected by the reflective means andtraveling back through the electro-optic crystal.

In the first form of the first mode of the first aspect of the presentinvention, the second electrode is a transparent film; the elastic filmis transparent, or has a plurality of beam portions extending radiallytoward the outside from the central portion; the reflective means is thebottom surface of the probing needle or a reflective film on the elasticfilm; the probing needle is attached at its bottom surface directly orvia the reflective means to the central portion of the elastic film; andthe voltage/phase-difference conversion means is also the displacementinformation generating means.

With this, the axial displacement of the probing needle can be detectedbased on a change in length of the path of the light beam travelingthrough the voltage/phase-difference conversion means, being reflectedby the reflective means and traveling back through thevoltage/phase-difference conversion means.

It becomes possible to use a common optical system for displacement andvoltage measurements to achieve a simplification of the structure andalso a simplification of the adjustment.

Also, it becomes possible to observe the sample with an opticalmicroscope by the reflected light from the sample the transparentelastic film or through between the beam portions in order to roughlydetermine a position of the probing needle relative to a voltagemeasuring point on the sample.

As described later, it is possible to use only one optical system, withdisplacement detection applying a strain gauge, or with displacementdetection applying a capacity, which also simplifies the adjustment.

In the second form of the first mode of the first aspect of the presentinvention, the elastic film is transparent, or has plural beam portionsextending radially toward the outside from the central portion, and alsothe first electrode; the first surface of the electro-optic crystal isbonded to the central portion of the elastic film; the probing needle isattached at its bottom surface to the second surface of theelectro-optic crystal directly or via the reflective means; and thevoltage/phase-difference conversion means is also the displacementinformation generating means.

This second form achieves similar advantages to those achieved in thefirst form.

In the third form of the first mode of the first aspect of the presentinvention, the second electrode is a reflective film and also thereflective means; the probing needle is attached at its bottom surfaceto the reflective film; the elastic film is transparent, or has aplurality of beam portions extending radially toward the outside fromthe central portion; and the lead has a portion connecting electricallybetween the first electrode and the elastic film; the voltage anddisplacement sensitive probe further comprising a rod being hollow orsolid and transparent, the rod being suspended vertically with an upperportion of the rod being bonded to the central portion of the elasticfilm; the voltage/phase-difference conversion means being bonded at thelower end of the rod with the tip of the probing needle downward.

This third form achieves similar advantages to those achieved in thefirst form.

As described below, it is possible to use only one optical system, withdisplacement detection applying a strain gauge, or with displacementdetection applying capacitance; which also simplify the adjustment.

In the second mode of the first aspect of the present invention, thedisplacement information generating means is a strain gauge which linksthe outer end of the elastic film with the holder.

With this arrangement, it is possible to detect the displacement of theprobing needle based on a change in the resistance value of the straingauge.

In the third mode of the first aspect of the present invention, thedisplacement information generating means includes; a first electricallyconductive plate an end of which is bonded to the rod with the other endbeing free; and a second electrically conductive plate, and end of whichis bonded to the holder with the other end being free, the secondelectrically conductive plate being located so as to face and the firstelectrically conductive plate.

With this, it is possible to detect displacement of the probing needlebased on a change in the capacitance between the first electricallyconductive plate and the second electrically conductive plate.

In the fourth mode of the first aspect of the present invention, thevoltage information generating means includes an electrically conductivetransparent film; a photoconductive film which upper surface is adheredto the electrically conductive film, the photoconductive film beingconnected electrically with the probing needle; and a lead for supplyingthe reference potential to the electrically conductive film.

With this arrangement, it is possible to detect the voltage of theprobing needle based on an electric current flowing in the lead when alight beam is irradiated on the photo conductive film.

In the fifth mode of the first aspect of the present invention, a firstmagnetic substance is attached in peripheral area of installationposition of the probing needle, wherein the probing needle has a secondmagnetic substance at least at its bottom portion.

With this arrangement, the probing needle can be held by the residualmagnetism of the first magnetic substance and the probing needle can bedropped with the demagnetization of the first magnetic substance.Therefore, when the tip of the probing needle has worn out, it is notnecessary to replace the entire probe, but only the probing needle,achieving a reduction in operating costs. Also, as automation of probingneedle replacement is possible, handling of the very small probingneedles becomes easier.

According to the second aspect of the present invention, there isprovided a voltage and displacement measuring apparatus comprises: thefirst mode of the first aspect of the present invention above, secondvoltage measuring means for measuring a voltage of the probing needlebased on a phase-difference between two vertical components of linearlypolarized light, the phase-difference being caused by the light beamtraveling through the electro-optic crystal, being reflected by thereflective means and traveling back through the electro-optic crystal;and displacement measuring means for measuring an axial displacement ofthe probing needle based on a change in the length of a path of thelight beam traveling through the voltage/phase-difference conversionmeans, being reflected by the reflective means and traveling backthrough the voltage/phase-difference conversion means.

In the first mode of the second aspect of the present invention, thevoltage and displacement measuring means comprises: a laser for emittingthe light beam; a beam splitter arranged so that the light beam entersthereinto, the beam splitter divides the light beam into penetratinglight and reflected light, one of which being directed into the voltage& displacement sensitive probe; a reflector arranged so that thereflector reflects the other one of the penetrating light and thereflected light back to the beam splitter; a polarization beam splitterarranged so that interfered light, composed of light which is from thereflector and traveling through the beam splitter or reflected by thebeam splitter and light which is from the probe and reflected by thebeam splitter or traveling through the beam splitter, enters thereintoand the polarization beam splitter divides the light beam intopenetrating light and reflected light; a first photodetector beingarranged so that the first photodetector detects the light penetratingthough the polarization beam splitter; a second photodetector arrangedso that the second photodetector detects the light reflected by thepolarization beam splitter; and a signal processing device that measuresthe axial displacement of the probing needle based on the displacementinformation which is either a first output signal from the firstphotodetector or a second output signal from the second photodetector,and measures the voltage of the probing needle relative to the referencepotential based on the voltage information which is a difference betweenthe first output signal and the second output signal.

The second mode of the second aspect of the present invention furthercomprises: an optical microscope having a barrel, an objective lensattached to the barrel, coarse movable stage and a fine movable stage,on which the barrel mounted, mounted on the coarse movable stage; and asecond holder, attached to the barrel, for holding the holder of thevoltage & displacement sensitive probe with the axis of the probevertically under the objective lens.

The third mode of the second aspect of the present invention furthercomprises: an optical microscope having a barrel, an objective lensattached to the barrel, coarse movable stage and a fine movable stage,on which the barrel mounted, mounted on the coarse movable stage; asecond fine movable stage mounted on the coarse movable stage; and asecond holder, attached to the second movable stage, for holding theholder of the voltage & displacement sensitive probe with the axis ofthe probe vertically under the objective lens.

The fourth mode of the second aspect of the present invention furthercomprises: an optical microscope having a barrel and an objective lensattached to the barrel; course movable stage; a fine movable stage, onwhich a sample is to be mounted, mounted on the coarse movable stage;and a second holder for holding the holder of the voltage anddisplacement sensitive probe with the axis of the probe vertically underthe objective lens.

According to the third aspect of the present invention, there isprovided a voltage and displacement measuring method, by using one ofthe above voltage and displacement measuring apparatus, comprising thesteps of: observing the sample with the optical microscope by thereflected light from the sample through the transparent elastic film orbetween the beam portions in order to determine roughly a position ofthe probing needle relative to a voltage measuring point on the sample;driving the fine movable stage so that the probe approach relative tothe sample until an amount of the axial displacement of the probingneedle relative to the holder is detected; measuring a surface positionof the sample in the axial direction of the probe based on the drivingdistance of the fine movable stage and the amount of the axialdisplacement of the probing needle relative to the holder; repeating thedriving and measuring steps at a plurality of positions in the planeperpendicular to the axial direction of the probe so as to decide finelythe voltage measuring point; driving the fine movable stage so that thetip of the probing needle comes close to or contacts to the voltagemeasuring point; and measuring a voltage at the tip of the probingneedle by the voltage measuring means.

In the first mode of the third aspect of the present invention, theapparatus comprises further a second fine movable stage, to which thereflector is attached, for moving the reflector in the direction ofreflection by the reflector, wherein after the step of contacting theprobing needle, the second fine movable stage is driven and stopped whenthe displacement detection sensitivity has become the maximum.

Other and further objects, features and advantages of the presentinvention will become apparent from the following description of thepreferred embodiments when the same is read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial sectional view of the voltage and displacementsensitive probe in the first embodiment according to present invention;

FIGS. 2A-2C are process diagrams of the production of the probing needlesupporter shown in FIG. 1;

FIG. 3 shows the operating state of the voltage and displacementsensitive probe in FIG. 1;

FIG. 4 shows the principle of displacement measurement applying thevoltage and displacement sensitive probe in FIG. 1;

FIG. 5 shows the principle of voltage measurement applying the voltageand displacement sensitive probe in FIG. 1;

FIG. 6 shows a voltage & displacement measuring apparatus mounted on anoptical microscope;

FIG. 7 shows another configuration of the voltage and displacementmeasuring apparatus mounted on an optical microscope;

FIG. 8 is an axial sectional view of the voltage and displacementsensitive probe in the second embodiment according to present invention;

FIG. 9A is a partial cutaway view of the voltage and displacementsensitive probe in the third embodiment,

FIG. 9B is an enlarged axial sectional view of the lower portion of FIG.9A, and

FIG. 9C is a perspective view of the cross beam and the upper portion ofthe rod in FIG. 9A;

FIG. 10A is a partial cutaway view of the voltage and displacementsensitive probe in the fourth embodiment,

FIG. 10B is an enlarged axial sectional view of the lower portion ofFIG. 10A and

FIG. 10C is a perspective view of the cross beam and the upper portionof the rod in FIG. 10A;

FIG. 11 is a strain/voltage conversion circuit diagram;

FIG. 12 shows a voltage and displacement measuring apparatus in thefourth embodiment according to the present invention mounted on anoptical microscope;

FIG. 13 is a fragmentary axial sectional view of the voltage anddisplacement sensitive probe in the fifth embodiment according to thepresent invention;

FIG. 14 shows a voltage and displacement measuring apparatus applyingthe probe shown in FIG. 13;

FIG. 15 is a flow chart showing the procedure with which the probingneedle is replaced;

FIG. 16 is a fragmentary axial sectional view of the voltage anddisplacement sensitive probe in the sixth embodiment according to thepresent invention;

FIG. 17 is an axial sectional view of the voltage and displacementsensitive probe in the seventh embodiment according to the presentinvention;

FIG. 18 is a fragmentary view of the lower portion of the voltage anddisplacement sensitive probe in the eighth embodiment according to thepresent invention; and

FIG. 19 is a schematic diagram of a voltage and displacement measuringapparatus to be considered for comparison with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout several views,embodiments of the present invention are described below.

First Embodiment

FIG. 1 shows an axial section of the voltage and displacement sensitiveprobe 30 in the first embodiment. This probe 30 is symmetrical withrespect to any plane through the axis thereof.

The holder 31 comprises a cylinder 31a whose diameter increases towardthe upper end from the bottom and the flange 31b which protrudes towardthe outside in the direction of the radius from the upper end of thecylinder 31a. The voltage/phase difference conversion device 32 isfitted in the holder 31.

The device 32 consists of an electro-optic crystal 32a whose upper andlower surfaces are parallel to each other, the electrically conductivetransparent film 32b which is adhered to the upper surface and theelectrically conductive transparent film 32c which is adhered to thelower surface. The electro-optic crystal 32a, corresponding to thevoltage between the electrically conductive transparent film 32b and32c, makes a phase difference between the two components of linearlypolarized light entering the upper surface at a right angle whoseelectric vector vibration directions are perpendicular to each other.The size of the electro-optic crystal 32a may be, for example, 1 mm indiameter and 1 mm in height.

The electrically conductive transparent film 32d is adhered to the innersurface of the holder 31 in order to apply ground potential from theoutside as a reference potential to the electrically conductivetransparent film 32b, and the lower end of the electrically conductivetransparent film 32d is continuous with the circumferential edge of theelectrically conductive transparent film 32b. The electricallyconductive transparent films 32b and 32d are formed, for example, by ITOdeposition with sputtering with the electro-optic crystal 32a fittedinside the holder 31.

The probing needle supporter 33 is fitted inside at the lower end of theholder 31. The probing needle supporter 33 consists of the frame 33a,the electrically conductive transparent film 33b whose circumferentialedge is bonded to the frame 33a and the electrically conductivetransparent film 33c which is continuous with the electricallyconductive transparent film 33b. The size of the electrically conductivetransparent film 33b may be, for example, 1 mm in diameter and 0.5 μmthick.

The electrically conductive transparent film 32e is adhered to the innersurface of the lower end of the holder 31 in order to connect betweenthe electrically conductive transparent films 33c and 32c, and the upperend of the electrically conductive transparent film 32e is continuouswith the circumferential edge of the electrically conductive transparentfilm 32c. The electrically conductive transparent films 32c and 32e areformed, for example, by ITO deposition with sputtering, with theelectro-optic crystal 32a fitted inside the holder 31.

An example of a production process for the probing needle supporter 33is shown in FIGS. 2A-2C.

First, as shown in FIG. 2(A), the electrically conductive transparentfilm 41 is adhered to the substrate 40 by sputtering. Then as shown inFIG. 2(B) an opening 42 is formed in the substrate by etching. Next, asshown in FIG. 2(C), ITO deposition is adhered to the frame 33a and theelectrically conductive transparent film 41 by sputtering from theopposite side of the electrically conductive transparent film 41.

In FIG. 1, the bottom surface of the probing needle 34 is bonded to thecentral area of the lower surface of the electrically conductivetransparent film 33b. The size of the probing needle 34 may be, forexample, 10 μm in diameter at the bottom surface and 10 μm in height.The probing needle 34 connects with the electrically conductivetransparent film 32c via the electrically conductive transparent films33b, 33c and 32e. As a result, when the tip of the probing needle 34contacts or approaches a sample such as a semiconductor chip 10 as shownin FIG. 3, the potential at the tip of the probing needle 34 is suppliedto the electrically conductive transparent film 32c. This potential willhave a value that corresponds to the potential at the measuring pointwhen the tip of the probing needle 34 approaches the surface of thesample and also corresponds to the capacitance between the measuringpoint and the tip of the probing needle 34.

In FIG. 1, the bottom surface of the probing needle 34 constitutes thereflective surface 34a and when the light beam L1 enters along the axisof the voltage and displacement sensitive probe 30, it travels throughthe voltage/phase difference conversion element 32 and the electricallyconductive transparent film 33b. It is then reflected by the reflectivesurface 34a and travels through the electrically conductive transparentfilm 33b and the voltage/phase-difference conversion element 32 again inthe reverse direction. By detecting the change in the length of thislight path, the displacement of the probing needle 34 relative to theholder 31, that is, the height of the contact or close point on thesample from a reference position can be detected.

FIG. 4 shows the principle of displacement measurement when the voltageand displacement sensitive probe 30 is used. In FIG. 4, the tip of theneedle 34 is in contact with the wire 13 on the semiconductor chip 10.

The Michelson interferometer 50 consists of the beam splitter 51 thatsplits the linearly polarized light beam L into the penetrating lightbeam L1 and the reflected light beam L2, the converging lens 52 forconverging the light beam L1 on to the bottom surface of the probingneedle 34, the mirror 53 for reflecting the beam L2 so that it willtravel in the reverse direction, and the photodetector 54 for detectingthe interfered light beam L3 consisting of the reflected light from themirror 53 which has passed through the beam splitter 51 and thereflected light from the probing needle 34 that has also been reflectedby the beam splitter 51. When the output from the photodetector 54 issupplied to the oscilloscope 55, the sine curve as shown in FIG. 4 isobtained on the screen display of the oscilloscope 55 during the processin which the voltage & displacement sensitive probe 30 is lowered so asto contact or approach the probing needle 34 to the wire 13. By countinga wave cycle of this sine curve, the displacement of the probing needle34 can be detected with an accuracy of about half the wavelength and bydetecting the phase of the waveform, this displacement can be detectedwith even high accuracy.

In FIG. 1, with the light beam L1 passing though the electro-opticcrystal 32a twice, the voltage at the tip of the probing needle 34 canbe measured by detecting the phase difference between the two componentsof linearly polarized light whose electric vector vibration directionsare perpendicular to each other. The principle of this measurement isshown in FIG. 5.

The phase difference detecting device 60 consists of the quarter-waveplate 61 that converts the linearly polarized light beam L to thecircularly polarized light beam L0, the beam splitter 51 into which thecircularly polarized light beam L0 enters, the converging lens 52 forconverging the penetrating light beam L1 from the beam splitter 51 onthe bottom surface of the probing needle 34, the polarization beamsplitter 62 into which the light beam L4 reflected by the beam splitter51, the photodetectors 54A and 54B which detect the light beam L5penetrating through the polarization beam splitter 62 and the light beamL6 reflected by the polarization beam splitter 62 respectively, and thedifferential amplifier 63 that amplifies the difference between theoutputs from the photodetector 54A and 54B. When the output from the ACvoltage source 64 is supplied to the wire 13 which is in contact withthe probing needle 34, and the outputs from the AC voltage source 64 andthe differential amplifier 63 are supplied to the oscilloscope 55, thevoltage waveform of the output from the AC voltage source 64 and thedifferential amplifier 63, as shown in FIG. 5, are obtained on thescreen display of the oscilloscope 55. Based upon the relationshipbetween the two waveforms, the voltage of the wire 13 can be measured.

In FIG. 1, by placing the voltage and displacement sensitive probe 30 onthe sample side of the objective lens of a optical microscope and byobserving the semiconductor chip 10 with the optical microscope throughthe voltage/phase difference conversion element 32 and the electricallyconductive transparent film 33b, the approximate position of the wiringon the semiconductor chip can be determined. The configuration of anapparatus, that applies the voltage and displacement sensitive probe 30and an apparatus applying principles of measurement shown in FIGS. 4 and5, mounted on an optical microscope, is shown in FIG. 6.

The semiconductor chip 10 is mounted via the package 14 on the circuitboard 15 for testing. Test signals are supplied via the circuit board 15and the package 14 to the semiconductor chip 10 from the signalprocessing device 70.

The voltage and displacement sensitive probe 30 is held by the probeholder 71 in such a manner that its optical axis is aligned with theoptical axis of the objective lens 52A, and the probe holder 71 iscoupled to a microscopic lens barrel. The microscopic lens barrel issupported via the fine movable X-Y-Z stage 72 by the coarse movableX-Y-Z stage 73. The fine movable X-Y-Z stage 72 is structured withpiezoelectric actuator and is capable of determining position with anaccuracy of 1/100 to 1/1000 μm and, at the same time, it is capable ofscanning in one direction through a range of several tens of μm. As aresult, with only the fine movable X-Y stage 72c and the fine movable Zstage 72d, a wiring pattern with a width and thickness of approximately1 μm on the semiconductor chip 10 can be scanned in detail and over asufficiently large range. When scanning the voltage and displacementsensitive probe 30C over a minimal range with the fine movable X-Y-Zstage 72, the coarse movable X-Y-Z stage 73 should be stopped.

The mirror 53 is bonded to one end of the fine movable X stage 74 whoselength in the direction of the reflected light beam L2 can be fineadjusted. The other end of the fine movable X stage 74 is bonded to asurface which is an integral part of the microscopic lens barrel. Theposition signals from the fine movable X-Y-Z stage 72, the coarsemovable X-Y-Z stage 73 and the fine movable X stage 74 are supplied tothe signal processing device 70. The controller 75 uses these positionsignals as feedback signals to drive the fine movable X-Y-Z stage 72,the coarse movable X-Y-Z stage 73 and the fine movable X stage 74.

The image that is formed by the objective lens 52A is then picked upthrough the pick-up lens 76 by the CCD image sensor 77 and its image isdisplayed on the monitor TV 78. The objective lens 52A also functions asthe converging lens 52 as shown in FIGS. 4 and 5.

The linearly polarized light emitted by the laser 28 is made parallel bythe collimator lens 79, reflected by the mirror 27 and then enters thequarter-wave plate 61. The quarter-wave plate 61, the beam splitter 51,the polarization beam splitter 62 and the photodetectors 54A and 54B areidentical to those shown in FIG. 5 and the mirror 53 is identical tothat shown in FIG. 4.

Regarding the measurement of displacement in the direction of height, asis obvious when compared to the structure shown in FIG. 4, the output SPwhich is either the output SA of the photodetector 54A or the output SBof the photodetector 54B corresponds to the output of the photodetector54 in FIG. 4. The signal processing device 70 measures the displacementof the probing needle 34 in the direction of height based upon this SP.The details of the concave-convex pattern on the semiconductor chip 10can be obtained based on the position signals from the fine movableX-Y-Z stage 72 and the coarse movable X-Y-Z stage 73 and thedisplacement of the probing needle 34 obtained from the SP.

As for the measurement of the voltage, it differs from the case in FIG.5 in that the reflected light from the mirror 53 is included in theinterference light beam L4A. However, since the reflected light from themirror 53 is circularly polarized and the intensities of the two lightbeams are equal after being divided into two by the polarization beamsplitter 62, the difference SM between the output SA of thephotodetector 54A and the output SB of the photodetector 54B is notaffected. The signal processing device 70 detects the voltage at the tipof the probing needle 34 based upon the difference SM.

The fine movable X-Y-Z stage 72 is driven to lower the voltage anddisplacement measuring probe 30 from the point over the wire which isthe object of the potential measurement on the semiconductor chip 10.After change in the SP is detected and further the change become equalto the set value, namely, after the probing needle 34 has contacted thewire on the semiconductor chip 10 or has come close to it, the loweringof the fine movable X-Y-Z stage 72 is stopped. Then the position of tipof the proving needle is found based on the driving distance of the finemovable X-Y-Z stage and the value of change in the SP.

In order to prevent the probing needle 34 from damaging the surface ofthe semiconductor chip 10 while the voltage & displacement sensitiveprobe 30 scans within the X-Y plane, the following measures may betaken: The height of the surface of the ship 10 at the time when the tipof the probing needle 34 has come close to or has contacted to thesurface of the chip 10 is detected in such a way as described above, andthe voltage & displacement sensitive probe 30 is driven in the direction+Z (upward) by a specific distance d. Next, it is driven within the X-Yplane and then driven in the direction -Z (downward) by the specificdistance d. This sequence of operations is performed repeatedly to scanthe surface of the semiconductor chip 10.

With the scanning described above, the voltage measuring point can beascertained accurately.

Next, the fine movable X-Y-Z stage 72 is driven so that the tip of theprobing needle 34 is close to or contacts to the voltage measuringpoint. It is preferable to stop the lowering of the fine movable X-Y-Zstage 72 when the SP has changed several cycles, for example, 10 cyclesbecause the contact of the probing needle 34 with the semiconductor chip10 becomes reliable.

Then the fine movable X stage 74 is driven and stopped when the SP hasreached the middle value between the maximum and the minimum values.With this, the displacement detection sensitivity is set to the maximum.

Then, the test signal is supplied to the semiconductor chip 10 toperform voltage measuring at this position.

With the voltage and displacement measuring apparatus that is structuredas described above, the voltage and the displacement measurements can bemade with a single optical system that applies on laser 28. Thus, thestructure and the required adjustments can be simplified compared to theprior art.

FIG. 3 shows the state in which the voltage and displacement sensitiveprobe 30 is used on the semiconductor chip 10. As can be clearly seen inFIG. 3, with the voltage and displacement sensitive probe 30 in thefirst embodiment according to the present invention, scanning can beperformed on the semiconductor chip 10 without interfering with thebonding wires 11 and 12.

FIG. 7 shows the voltage and displacement measuring apparatus installedin an optical microscope with a different configuration. This device isstructured so that the semiconductor chip 10 is moved instead of theoptical microscope. In other words, the circuit board 15 is mounted viathe fine movable X-Y-Z stage 72A on the the coarse movable X-Y-Z stage73. All other aspects are identical to the case shown in FIG. 6.

With this structure, since the sample, whose inertia is small incomparison to that of the microscope, can be driven at high speed, thetime required for measuring can be reduced.

Second Embodiment

FIG. 8 shows an axial sectional view of the voltage & displacementsensitive probe 30A in the second embodiment. This probe 30A issymmetrical with respect to any plane through the axis thereof.

The upper surface of the electro-optic crystal 32a is bonded to thecentral portion of the lower surface of the electrically conductivetransparent film 33b and the bottom surface of the probing needle 34 isbonded to the lower surface of the electro-optic crystal 32a. Theelectro-optic crystal 32a may be, for example, 10 μm in diameter and 10μm in height.

The electrically conductive transparent film 33b and the probing needle34 form a pair of electrodes for the electro-optic crystal 32a. Theholder 31A is structured with an electrically conductive material, whichis connected with the electrically conductive transparent film 33b.

Accordingly, the structure of the voltage & displacement sensitive probe30A is simpler than that of the voltage and displacement sensitive probeshown in FIG. 1.

All other aspects are identical to those in the first embodimentdescribed earlier.

Third Embodiment

FIG. 9A shows a partial cutaway through the axis of the voltage &displacement sensitive probe 30B in the third embodiment. This probe 30Bis symmetrical with respect to four planes through the axis thereof.

In the rod 80, as shown in FIG. 9B, the electrically conductivetransparent films 80b and 32b are adhered to the side surface and thebottom surface, respectively, of the solid transparent glass rod 80a andthe anti-reflection film 80c is adhered to the upper surface of the rod80. The size of the rod 80 may be, for example, 0.4 mm in diameter and 5mm in length. The upper surface of the electro-optic crystal 32a isbonded to the lower surface of the rod 80. The reflective film 32f isadhered to the lower surface of the electro-optic crystal 32a and tothis film 32f, the bottom surface of the probing needle 34A is bonded.

As shown in FIG. 9C, the upper end of the rod 80 is bonded to thecentral portion 810 of the cross beam 81. The hole 81a, which isconcentric with the rod 80, is formed in the central portion 810. Thecross beam 81 is formed of the central portion 810 and band portions 811and 814 that extend radially in four directions from the central portion810. The tips of the band portions 811 to 814 are bonded to the bottomsurface of the holder 82. Observation with an optical microscope isperformed through the areas between the band portions 811 to 814, whichare inside the holder 82.

The cross beam 81 is electrically conductive and elastic and may beformed of, for example, aluminum. Its size is 20 μm thick, 3 mm indiameter and 0.4 mm in width of each the band portion 811 to 814. Theprobing needle 34A is, for example, 50 μm in diameter at the upper plateportion, and 400 μm in height. It is not restricted to a four cross beamscheme; a three or even two beam scheme is sufficient in some cases.

The electrically conductive transparent film 32b connects with theelectrically conductive holder 82 via the electrically conductivetransparent film 80b and the electrically conductive cross beam 81.

The light beam L1 that has entered the central area of the upper end ofthe rod 80 at a right angle, travels through the rod 80 and theelectro-optic crystal 32a, is reflected by the reflective film 32f andthen travels the same path in reverse.

All other aspects are identical to those in the first embodimentdescribed earlier.

Fourth Embodiment

FIG. 10A is a partial cutaway view of the voltage & displacementsensitive probe 30C in the fourth embodiment, FIG. 10B is an enlargedaxial sectional view of the lower portion of FIG. 10A and FIG. 10C is aperspective view of the cross beam 81 and the upper portion of the rod80A in FIG. 10A.

This probe 30C is symmetrical with respect to four planes through theaxis thereof. The rod 80A is hollow. The tips of the band portions 811to 814 of the cross beam 81 are bonded to the bottom surface of theholder 82 via the strain gauges 831 to 834. The electrically conductivetransparent film 32b connects with the holder 82 via the electricallyconductive rod 80A and the cross beam 81.

FIG. 11 shows the principle structure of a strain/voltage conversioncircuit (Wheatstone bridge circuit) in the known art. This circuitconverts the change in resistance of the strain gauge 831 into anunbalanced voltage ΔV and then amplifies it by the differentialamplifier 84.

In case the cross beam 81 is made of aluminum and its size is 20 μmthick, 3 mm in diameter and 0.4 mm in width of each the band portion 811to 814 as described above, if the central portion 810 is displaced inthe direction of the height by 10 nanometers, the strain at thepositions of the strain gauges 831 to 834 is approximately 0.2×10⁻⁶. Thegauge factor of the semiconductor strain gauge is approximately 100 andif the DC voltage applied to the bridge is 10 V, the change in theunbalanced voltage ΔV will be 0.1 mV. Since voltages can be measuredwith a resolution of approximately 10 μV, displacement in the height ofthe probing needle 34A can be measured with sufficient accuracy.

FIG. 12 shows a structure in which the voltage & displacement sensitiveprobe 30A shown in FIG. 10 and the apparatus that applies the principlesof measurement illustrated in FIGS. 5 and 11 are mounted in an opticalmicroscope.

This structure does not use the mirror 53 and the fine movable X stage74 shown in FIGS. 6 and 7. Instead, it has the strain/voltage conversioncircuit internally provided in the signal processing device 70A tomeasure the displacement of the tip of the probing needle 34A in thedirection of height.

Also, the probe holder 71B can make fine movable independent of theoptical microscope. In other words, the microscopic lens barrel ismounted via the fine movable X-Y stage 72a and the fine movable Z stage72b to the coarse movable X-Y-Z stage 73. Likewise, the probe holder 71Bis mounted via the fine movable Z stage 72c and the fine movable X-Ystage 72d to the coarse movable X-Y-Z stage 73.

Since the total mass of the probe holder 71B and the voltage &displacement sensitive probe 30C is sufficiently small in comparisonwith the mass of the optical microscope, the scanning on the sample 10can be at high speed, and as a result, the time required for measuringcan be reduced.

All other aspects are identical to those in the first embodimentdescribed earlier.

Fifth Embodiment

FIG. 13 shows a fragmentary axial sectional view of the lower portion ofthe voltage sensitive probe 30D in the fifth embodiment. This lowerportion is symmetrical, excluding the lead wire 85, with respect to anyplane through the axis thereof.

The lower end portion of the rod 80B is constituted by the magneticcylinder 86 and the electro-optic crystal 32a is fitted inside themagnetic cylinder 86. The magnetic cylinder 86 may be formed of, forexample, ferrite and its size is 1.5 mm in external diameter, 1 mm ininternal diameter and 1.5 mm in height. The rod 80B is an insulatorexcept the magnetic cylinder 86 and the lead wire 85 is formed on itsinner wall. The lead wire 85 connects between the electricallyconductive transparent film 32b and the cross beam 81 shown in FIG. 10A.

The reflective film 32g is adhered to the central portion of the bottomsurface of the electro-optic crystal 32a and the reflective film 32g isan separate entity from the probing needle 34b. The magnetic film 87,which may be, for example, a ferrite film, is adhered to the bottomsurface of the probing needle 34B. The structure of the voltage anddisplacement sensitive probe 30D is otherwise identical to that shown inFIG. 10.

FIG. 14 shows the structure of the voltage and displacement measuringapparatus that applies the voltage and displacement sensitive probe 30D.

The voltage and displacement sensitive probe 30D is mounted on the probeholder 71C and, similar to the configuration shown in FIG. 12, it issupported via the fine movable X-Y stage 72c and the fine movable Zstage 72d on the coarse movable X-Y-Z stage 73. The probing needlereplacing device 90 is provided on the outside of the light path of theprobe 30D.

In the probing needle replacing device 90, the coil 91 is provided withits axis vertically. The inner diameter of the coil 91 is larger thanthat of the rod 80B. The movable stage 92 is provided under the coil 91and the tray 93 is mounted on the movable stage 92. A plurality of holesare formed in the vertical direction in the tray 93 and the tip portionsof the probing needles 34B are inserted to these holes to hold theprobing needles 34B vertically. The light source 94 and photodetector 95for detecting the lowering and raising of the probing needle 34B areprovided facing each other between the tray 93 and the coil 91. The coil91 is tuned on/off by the controller 75B via the driver 96, the movablestage 92 is driven by the controller 75B and the detection signal fromthe photodetector 95 is supplied to the controller 75B.

The following is the explanation of the replacement procedure for theprobing needle 34B in reference to FIG. 15. Hereafter, numbers inparentheses indicate the step numbers in FIG. 15.

(100) The coarse movable X-Y-Z stage 73 is driven so that the opticalaxis of the voltage & displacement sensitive probe 30D is aligned withthe axis of the coil 91. Then, the lower end portion of the voltage anddisplacement sensitive probe 30D is inserted within the coil 91.

(101) The movable stage 92 are driven so that the empty hole on the tray93 is aligned with the axis of the coil 91.

(102) The magnetic cylinder is demagnetized by an electric currentthrough the coil 91 and the lowering of the probing needle 34B isdetected with the photodetector 95. With tis lowering, the probingneedle 34B is held in the hole on the tray 93.

(103) The position of the hole in which the new probing needle 34B forreplacement is inserted on the tray 93 is aligned on to the axis of thecoil 91.

(104) The magnetic cylinder 86 is magnetized by an electric current tothe coil 91 to bond the magnetic film 87 of the probing needle 34B tothe reflective film 32g. After detecting the going-up probing needle 34Bby the photodetector 95, the electric current to the coil 91 is turnedoff. Even when the electric current is turned off, the probing needle34B remains adhered to the reflective film 32g with the residualmagnetism of the magnetic cylinder 86.

(105) The coarse movable X-Y-Z stage 73 is driven to move the voltageand displacement sensitive probe 30D to the initial position.

In the manner described above, the probing needle 34B can be replacedautomatically. The operator should observe the tip configuration of theused probing needle 34B and relate it to the degree of use.

It is understood that the magnetic film may be adhered to the reflectivefilm 32g. Also, the probing needle 34B may be another one as shown FIG.9B.

Sixth Embodiment

FIG. 16 shows an axial sectional view of the lower portion of thevoltage and displacement sensitive probe 30E in the sixth embodiment.This lower portion applies a photoconductive gate and is symmetrical,excluding the lead wire 85, with respect to any plane through the axisthereof.

The photoconductive film 111 is adhered to the lower surface of thetransparent substrate 110 via the electrically conductive transparentfilm 32c and the transparent substrate 110 is fitted inside the magneticcylinder 86. The electrically conductive transparent film 32c isconnected via the lead wire 85 that runs along the inner wall of the rod80B, the cross beam 81 and the holder 82 shown in FIG. 10 to the currentdetection circuit 112 shown in FIG. 16. The current detection circuit112 detects the electric current that flows in the lead wire 85,converts it to a voltage, amplifies it and then outputs it.

In the structure described above, when the light beam L1 enters into therod 80B, it radiates on to the photoconductive gate film 111 through thetransparent substrate 110 and the electrically conductive transparentfilm 32c to lower the resistivity at the irradiated point. Thus, anelectric current that value corresponds to the voltage between theprobing needle 34B and the electrically conductive transparent film 32cflows in the lead wire 85 to be detected by the current detectioncircuit 112.

In the sixth embodiment, the current detection circuit 112 is usedinstead of the device shown in FIG. 5 and the optical system can beconstituted with the laser and the mirror for reflecting the laser beamto direct it into the rod 80B, thereby making the structure of theoptical system particularly simple. All other aspects are identical tothose in the fifth embodiment described earlier.

Seventh Embodiment

FIG. 17 shows a partial axial cutaway view of the voltage & displacementsensitive probe 30F in the seventh embodiment. This voltage anddisplacement sensitive probe 30F is symmetrical with respect to pluralplanes through the axis thereof.

The rod 80A and the portion that is mounted at its lower end have thesame structures as those shown in FIG. 10. The holder 82A corresponds tothe holder 82 in FIG. 10 and the outer ends of the cross beams 81A, 81Beach of which is identical to the cross beam 81 in FIG. 10, are bondedto the inner circumferential surface of the holder at the upper portionand the lower portion respectively, and the inner ends of the crossbeams 81A, 81B are bonded to the external circumferential surface of therod 80A. Between the cross beam 81A and the cross beam 81B, the innerend of the electrically conductive plate 97 is bonded perpendicular tothe external circumferential surface of the rod 80A, and the outer endsof the electrically conductive plates 98 and 99 are bonded perpendicularto the inner circumferential surface of the holder 82A at a distancefrom the electrically conductive plate 97 in such a manner that theyenclose the conductive plate 97 in order to detect a change incapacitance as the displacement of the rod 80A in the direction of theaxis. In order to enable observation of the sample with an opticalmicroscope through the inside of the the holder 82A, the electricallyconductive plates 97, 98, 99 may be, for example, cross-shaped, similarto the cross beams 81A and 81B. A capacitance detection circuit that isconnected to the electrically conductive plates 97, 98, 99 via a leadwire (not shown) may be a Wheatstone bridge circuit of the known art.

All other aspects are identical to those in the fourth embodimentdescribed earlier.

Eighth Embodiment

FIG. 18 shows the lower portion of the voltage and displacementsensitive probe 30G of the eighth embodiment. This lower portion is usedinstead of the rod 80A and what is installed at its lower end in FIG.17. It is symmetrical, excluding the lead wire 85, with respect to aplurality of planes through the axis thereof.

A photoconductive gate, which is structured similarly to that shown inFIG. 16, is mounted to the lower end of the rod 80. Namely, the probingneedle 34 is bonded on to the lower end of the rod 80 via thetransparent substrate 110, the electrically conductive transparent film32c and the photoconductive film 111. The transparent electricallyconductive film 32c is connected to the lower end of the lead wire 85that extends over the external circumferential surface of thetransparent substrate 110 and the rod 80 in the direction of the axis.

Having described specific embodiments of the present invention, it is tobe understood that modification and variation of the invention arepossible without departing from the spirit and scope thereof.

What is claimed is:
 1. A voltage & displacement sensitive probecomprising:a holder having a hole arranged approximately symmetricalwith respect to plural planes through the axis thereof; a rod beinghollow or solid and transparent; first and second elastic films bridgingbetween said holder and said rod and supporting said rod vertically,said second elastic film being located beneath said first elastic film;an electro-optic crystal, first and second surfaces of which areparallel to each other and arranged vertically to the axis of said hole;a first electrode consisting of a transparent film adhered to said firstsurface and bonded to the lower end of said rod; a second electrodeadhered to said second surface and connected electrically with saidprobing needle, said second electrode reflecting a light beam travellingfrom said first electrode through said electro-optic crystal and back;an electrically conductive probing needle being attached at its bottomsurface to said second electrode, a tip of said probing needle pointingdownward; a first electrically conductive plate, an end of which isbonded to said rod with the other end being free; and a secondelectrically conductive plate, an end of which is bonded to said holderwith the other end being free, said second electrically conductive platefacing said first electrically conductive plate.
 2. A voltage anddisplacement sensitive probe according to claim 1, wherein said rod iselectrically conductive and is electrically connected to said firstelectrode, and said first or second elastic film is electricallyconductive.
 3. A voltage and displacement sensitive probe according toclaim 2, wherein each of said first and second elastic films is a crossbeam.
 4. A voltage and displacement sensitive probe according to claim3, further comprising a third electrically conductive plate, an end ofwhich is bonded to said holder with the other end being free, said thirdplate facing said first plate with said first plate being between saidsecond and third plates.
 5. A voltage and displacement sensitive probecomprising:a holder having a hole being approximately symmetrical withrespect to a plurality of planes through the axis thereof; anelectro-optic crystal arranged concentrically with said hole, first andsecond surfaces thereof being parallel to each other; an electrodeadhered to said first surface; a reflector for reflecting back incidentlight beam thereon travelled through said electro-optic crystal along anaxis of said hole, said reflector being formed on said second surface;an electrically conductive probing needle coupled to the central portionof said second surface with a tip of said probing needle pointingdownward; a rod, which permits light to pass through, bonded to saidelectrode at the bottom thereof; and an elastic film arranged inside ofsaid hole, the outer end thereof being bonded to said holder whilekeeping a strain thereon, said rod being suspended at a central portionof said elastic film, said elastic film being approximately symmetricalwith respect to a plurality of planes through the axis of said hole. 6.A voltage and displacement sensitive probe according to claim 5, whereinsaid rod is electrically conductive, and is electrically connected tosaid electrode, and said elastic film is electrically conductive.
 7. Avoltage and displacement sensitive probe according to claim 6, furthercomprising:a first electrically conductive plate, an end of which isbonded to said rod with the other end being free; and a secondelectrically conductive plate, an end of which is bonded to said holderwith the other end being free, said second plate facing said firstplate.